Polymorphism of 2‑Adamantanone

The
polymorphism of 2-adamantanone (C10H14O) has
been investigated by means of X-ray diffraction and high-pressure
thermal analysis. The intricate behavior of the low-temperature crystalline
phases has been disentangled. The stable phase has been found to be
orthorhombic (Cmc21, Z = 4), fully ordered, with lattice parameters a =
6.8884(18) Å, b = 10.830(3) Å, c = 10.658(3) Å, and V/Z = 198.8(1) Å3. The metastable phase was determined
to be monoclinic (P21/c, Z = 4) with lattice parameters a = 6.5920(17) Å, b = 11.118(3) Å, c = 12.589(3) Å, β= 118.869(11) o,
and V/Z = 202.0(1) Å3. The pressure–temperature phase diagram irrefutably shows
the stability relation between both phases and, accordingly, the long-time
unknown polymorphic behavior is now revealed and gives coherent physical
explanation of the literature published so far.